Electrophotographic marking is a well-known and commonly used method of copying or printing documents. Electrophotographic marking is performed by projecting a light image representation of a desired document onto a substantially uniformly charged photoreceptive member. In response to exposure to the light image representation, the photoreceptive member discharges so as to create an electrostatic latent image of the desired document. A development material having pigmented toner is then deposited onto the electrostatic latent image so as to form a toner image. The toner image is next transferred from the photoreceptor onto a substrate such as a sheet of paper. The transferred toner image, supported by the substrate, is fused into the substrate to form the completed printed document. Fusing of the toner image to the substrate is typically accomplished by a combination of heat and/or pressure. The surface of the photoreceptive member is then cleaned of residual developing material and recharged in preparation for production of a subsequent document.
The developing material can be formed of dry pigmented marking or toner particles attracted to the latent image areas to create a powder toner image on the photoreceptive or imaging member. Alternatively, a liquid developing material can be employed having charged pigmented marking particles immersed in a liquid carrier. The charge on the marking particles is created by a soluble ionic surfactant or charge director material dispersed or dissolved in a liquid carrier. The result is an electrochemical reaction that pruduces an exchange of ionic species between the marking particles and the micelles formed by the charge director. The liquid developing material is applied to the surface of the latent image-bearing member with the charged particles electrophoretically precipitated from the liquid developing material dispersion so as to migrate and be deposited on the image areas of the latent image. The migration and deposition of the toner particles forms the developed toner image.
In either dry powder toner development or liquid toner development arrangements, the image is developed onto the photoreceptive member. The toner image is subsequently transferred to the substrate for fusing. However, in certain circumstances, the toner image can incompletely transfer from the photoreceptive member to the substrate. The incomplete transfer can be due to the material or texture of the substrate. The incomplete transfer can also arise, for example, from low conformability of the photoreceptive member. Improved conformability can allow transfer of the toner image to relatively rough or different material substrates. Therefore in some circumstances, the toner image is first transferred to an intermediate transfer member having improved properties for the transfer of the toner image to the final substrate. Typically an improved property is increased conformability relative to a photoreceptor. However, this results in the necessity for an intermediate member and transfer of the toner image from the photoreceptive member to the intermediate member and then from the intermediate member to the substrate. Each transfer of the toner image has the potential for deterioration in quality of the toner image.
One form of electrophotographic printing employed to avoid these prior difficulties is ionographic printing where an electrostatic image is formed on an image-bearing member by an ion beam. The image bearing member is employed to avoid conformability of a photoreceptor but without additional transfers of the toner image. However, ionographic printing can have poor image quality, resulting from a phenomenon described as image blooming. In image blooming previously deposited ions can displace the subsequent ions directed to the charge retentive surface. This results in blooming or blurring of the image and therefore decreased image definition. This problem is particularly noticeable when printing characters and printing the edges of solid areas. Blooming defects may include picture elements being displaced by up to one or two pixel diameters. Image blooming can also result from poor charge retention on the image-bearing member. Furthermore, image blooming can result from charge migration in the electrostatic latent image formed on the image-bearing member. These problems are particularly prevalent for focused beam ion sources where the focused beam ion source is utilized for image-wise charging of a latent imagebearing member.